One prior-art plug for eliminating troublesome zones in wells is known to comprise a plugging agent in the form of a dry quick-setting mixture packed in an elastic water-proof cylindrical chamber having a diameter equal to the diameter of the well, the bottom end of said chamber being stoppered, while the top end is adapted to tightly close said chamber after said plugging agent has been packed therein.
In the known prior-art plugs the chamber thereof is closed by tying up, or by welding, or else by pasting the top end of the chamber along the boundary line of the plugging agent (cf., e.g., A Collection of Proceedings of the All-Union Research Institute for Prospecting Methods and Techniques entitled "Prospecting methods and techniques", No. 114, 1977, Leningrad, pp. 67-69).
When lowering the plugs down the well into the troublesome zone thereof, the dry quick-setting mixture is liable to get compacted as a result of its being exposed to the effect of high pressures and to all-round compression by the surrounding fluid.
As a result the air found in the mixture, is liable to accumulate into bubbles that destruct the walls of the chamber of the known plug before application of the mixture.
This leads to a premature hydration of the dry quick-setting mixture before its application in the troublesome zone of the well, its dilution (i.e., reducing a required concentration thereof) and to losing its activity and plugging ability.
All this contributes to overexpenditure of plugging agents and affects adversely the quality and productivity of sealing jobs involved in eliminating troublesome zones in wells.